Patients being admitted to the orthopaedic service at the Dartmouth-Hitchcock Medical Center for insertion or removal of a metallic appliance are being studied for the presence of metal allergy. The leucocyte migration test in agarose is our test method for detecting allergy to Ni, Co, or Cr. The allergic status of the patient will then be correlated with the clinical history. The importance of either pre-existing allergy or acquired allergy in clinical complications will then be determined. The implants removed from these patients are being analyzed for evidence of corrosion, abrasion, or other damage, and for the quality of the alloy. The role of alloy, quality of the alloy, and any evidence of metal loss from the implant will then be correlated with the patient's clinical history and the presence or absence of metal allergy. Animal models are also being developed using the rabbit and the guinea pig. These animals are made sensitive to Ni, Co, or Cr by injection and then bone screws are implanted. The histologic response to the bone screw is then compared to that of uninjected animals receiving bone screws. With the animal models and the human study the significance of metal allergy in reactions to orthopaedic implants can be assessed.